1. Field of the Invention
The present invention relates to a vibrator. Particularly, it relates to a vibrator used in an apparatus utilizing vibration such as a vibrating gyroscope or an angular velocity sensor, used in detecting shaking of hands in a video camera or the attitude control for an automobile.
2. Description of the Prior Arts
FIG. 26 is a perspective view showing an example of a conventional vibrator, and FIG. 27 is a transverse sectional view thereof. The vibrator 1 includes a regular triangle columnar vibrating body 2 consisting of a constant elastic metal material such as elinvar, and at the center of three side faces of the vibrating body 2, stripped piezoelectric element 3a, 3b and 3c are bonded respectively. That is, the piezoelectric element 3a consists of electrodes 5a and a formed on both surfaces of a piezoelectric layer 4a, with one electrode 5a being bonded to one side face of the vibrating body 2. Similarly, the piezoelectric elements 3b and 3c respectively consist of electrodes 5b, 6b and 5c, 6c formed on both surfaces of piezoelectric layers 4b and 4c, with one electrodes 5b and 5c being bonded respectively to the other two side faces of the vibrating body 2. The vibrating body 2 is supported by a supporting member in the neighborhood of its nodal point.
When using the vibrating gyroscope, for example, one piezoelectric element 3a is used for feedback and the other two piezoelectric elements 4b and 4c are used for driving and detection, and furthermore, the vibrating body 2 is grounded.
FIG. 28 is a circuit diagram showing an example of such a vibrating gyroscope.
That is, in the vibrating gyroscope 7, the other electrode 6a of the piezoelectric element 3a for feedback of the vibrator 1 constitutes a portion of a feedback loop for driving the vibrator 1, and through an inversion amplifier circuit 8 having an operational amplifier 8a, is connected, for example, to the input side of a phase correcting circuit 9 consisting of a 2-stage RC filter. The output side of the phase correcting circuit 9 is connected respectively to the electrodes 6b and 6c of the other piezoelectric elements 3b and 3c, through fixed resistances 10a and 10b. The vibrating body 2 of the vibrator 1 is grounded by an earth terminal 11 made of a metal. Meanwhile, the electrodes 6b and 6c of the two piezoelectric elements 3b and 3c are connected respectively to a non-inversion input end and an inversion input end of a differential amplifier 12.
In the vibrating gyroscope 7, since the output from the piezoelectric element 3a is fed back to the two piezoelectric elements 3b and 3c through the inversion amplifier circuit 8 and so on, the vibrator 1 is subjected to self-oscillation.
Then, in this state, when the vibrator 1 is rotated about its axis, a voltage corresponding to its rotational angular velocity is produced between the two piezoelectric elements 3b and 3c. This voltage is detected in the differential amplifier 12 and outputted.
Accordingly, in the vibrating gyroscope 7, the rotational angular velocity can be known by the output of the differential amplifier 12.
However, in the aforesaid vibrator 1, since the piezoelectric elements 3a-3c are bonded to the vibrating body 2, it is difficult to make it in a very small size. That is, in case of making the vibrating body 2 too small, the piezoelectric elements 3a-3c can not be bonded accurately at the center of the side faces of the vibrating body 2.
Also, in the vibrator 1, since a constant elastic metal material is used as the vibrator body 2, it is very costly.
Moreover, the coefficients of thermal expansion of the vibrating body 2 and the piezoelectric elements 3a-3c are different, so that variations occur at the bonded portion due to changes in atmospheric temperature, thereby causing characteristic variations.
In addition, for driving the vibrator 1, not only the vibrating body 2 must be grounded, but also the phase correcting circuit is necessary in a feedback loop for driving, the circuit configuration becomes complicated.